How does a lightbulb make light?

It depends which type of bulb you mean... The 'energy saver' ones - are miniature fluorescent bulbs - they have a light-emitting coating on the inside, which is 'stimulated' by Mercury vapour created when the power flows through it. The older 'pearl' bulbs work by the resistance of a wire filament inside the bulb causing it to glow as it heats up.